Gavia immer
common loon
(Also: great northern diver)

This species is most abundant in Canada and the Northern United States. Common loons breed on lakes and other waterways from western Greenland west across Canada and the northernmost United State, including Alaska. They winter along both coasts of North America as far south as Baja California and Texas. There is a breeding population on Iceland, and the species is a frequent winter visitor to the western coasts of Europe.

Loons nest on lakes and large ponds. Weather restricts habitat selection, because loons cannot nest on frozen water. They prefer to nest offshore, on islands, islets, or floating mounds of vegetation in shallow water. In winter, loons migrate to shallow coastal marine habitat.

Common loons are large swimming birds with long bodies (70 to 90 cm long, 1.6 to 8.0 kg) that sit low in the water. They have straight, thick, "daggerlike" bills that are black in the breeding season and gray during the rest of the year. The plumage of loons is black, white and gray. During the breeding season, common loons have a black head with a white and black barred necklace, and a checkered pattern on their back. During the winter, they are evenly gray on the head and back, with a white neck and underside. The common loon can be distinguished from other loons by its unique plumage patterns during the breeding season and black bill. During the winter, common loons can be distinguished by the indentation of the white neck color at mid-neck. Common loons are also larger than most loon species, excluding yellow-billed loons.

Male and female common loons look alike, though males are usually larger than the females. Young common loons look similar to winter adults, but have more white on their head and back. This juvenile plumage is maintained through their first summer. (McIntyre and Barr, 1997; National Geographic Society, 1987; Peterson and Peterson, 2002; Robbins, Bruun, and Zim, 2001)

Common loons are thought to be relatively long-lived birds. However, there is little information available about common loon survivorship. The oldest known wild common loon lived at least 9 years. ("The Sibley Guide to Bird Life and Behavior", 2001; "USGS Upper Midwest Environmental Sciences Center", 2003)

During the breeding season, most loons are found in breeding pairs. However, small flocks of unmated individuals and unsuccessful breeders may also be seen during the breeding season. The breeding territory of loon pairs ranges from 0.24 to 0.81 square kilometers.

Common loons are migratory, leaving their breeding grounds beginning in September. They migrate by day, singly or in flocks of up to 15 individuals. During migration, loons may spend the nights in flocks of several hundred individuals on large inland lakes. On their wintering grounds, individuals defend small feeding territories of 0.04 to 0.08 square kilometers during the day, but flock together at night.

Common loons are specialized swimmers. Their legs are placed very far back on their bodies, making them very powerful underwater swimmers. However, this arrangement also makes walking difficult for these birds. ("The New Encyclopedia of Birds", 2003; "The Sibley Guide to Bird Life and Behavior", 2001; Stokes and Stokes, 1983)

Common loons use visual displays and vocalizations to communicate. Stokes and Stokes (1983) identified six visual displays and five types of vocalizations used by common loons. These displays and vocalizations are used in courtship, territorial disputes, communication between pairs and offspring, and between flock members, and to signal alarm. (Stokes and Stokes, 1983)

Loons eat fish and other aquatic animals, including crayfish, shrimp, leeches and some aquatic vegetation. Minnows are good-sized food for young, which also eat insects occasionally.

Loons are visual predators, locating fish by sight and diving deep to catch them. They generally hunt in water 2 to 4 meters deep. Because they rely on sight, clear water is critical to common loons. Adult loons ingest most of their food items underwater where they catch them. They bring larger items to the surface before eating them.

Loons drink water by scooping it up with their bill and tilting their head back in order to swallow. (McIntyre and Barr, 1997)

Adult loons have few known predators, but may be vulnerable to large marine mammals such as sea otters and large raptors, such as bald eagles and ospreys. Gulls, crows, ravens, bald eaglesraccoons, skunks, minks and weasels, snapping turtles and large fish are predators of loon eggs and chicks.

Loons avoid predation by nesting on islands, where ground-based predators are less common. When approached by a predator, loons sometimes attack the predator by rushing at it and attempting to impale it through the abdomen or the back of the head or neck. ("The Sibley Guide to Bird Life and Behavior", 2001; McIntyre and Barr, 1997)

Common loons are provide food for their predators. They are also host to at least forty different body parasites. Most of these are cestodes and trematodes.

Because common loons eat fish, they are viewed by some people as competition for fishermen.

Common loons are a source of food to the Cree Indian tribe of Canada. They were once hunted for sport, and are now an important symbol of wilderness to many people.

Common loons are threatened primarily by habitat loss and/or degradation. Loons are highly sensitive to human disturbance through recreation or development on formerly secluded lakes. They are also threatened by industrial pollutants, such as mercury and other heavy metals that accumulate in the loons' bodies and slowly poison them. Acid rain kills phytoplankton, collapsing the aquatic food chains that loons depend on for food.

Oil spills are deadly to loons, which are unable to fly, dive or swim when their plumage becomes saturated with oil. Lead poisoning from ingestion of lead sinkers and entanglement in fishing nets are other sources of mortality.

Common loons are not considered federally endangered or threatened. However, they do have special conservation status in some states, including Michigan, where they are listed as threatened. They are also protected by the U.S. Migratory Bird Act. ("The Sibley Guide to Bird Life and Behavior", 2001)